In addition to transistors, other devices such as resistors, capacitors and diodes are formed during the manufacture of integrated circuits. These devices may be used to set voltage levels, pass or block signals, and form delay paths. In some cases these devices may be used to measure temperature.
The equation for the resistance of resistor material as a function of temperature is given by the equationRTEMP=R0+C1ΔT+C2(ΔT)2 Where R0 is the resistance at a reference temperature such as room temperature, C1 is the linear temperature coefficient of resistance, C2 is the quadratic temperature coefficient of resistance, and ΔT is the difference between ambient temperature and the reference temperature.
Because the resistance of metals commonly used in integrated circuits such as copper and aluminum has low resistance, when a temperature sensing resistor is needed, a high resistance metal such as nickel or molybdenum is added to the integrated circuit process flow to form the temperature sensing resistor. Addition of a new metal to the manufacturing flow adds cost by requiring additional deposition and etching manufacturing steps.